What kind of injuries would a soldier have to sustain to end up permanently blinded? Would, say, them being near an explosion work/be plausible?

Yes. Anything that damages the eye has a potential to result in permanent blindness, this includes shrapnel from a blast. Eyes can also be burned with intense heat, damaged via chemical exposure.

Now… your character’s probably going to have some scaring on their face in addition to being blind, but it is quite possible.

-Starke

perspi-looks said: Not to mention anything that causes a hit to the head, which means your brain can knock against your skull. Damage to the visual centers or optical nerves could happen that way, which may leave your character blind without much facial scarring.